Collision course with humanity

AS Donal Hickey reported on this page last week, a sea-eagle has been killed by a turbine blade in Kerry.

Wind-farms are a new hazard but flying has long been a risky business; birds crash into lighthouses on foggy nights and countless others die on the roads. Glass-fronted buildings can also be lethal.

In 2004, a flock of waxwings roosted near an office-block in St Stephen’s Green in Dublin. The little Scandinavian visitors kept crashing into windows. At least a dozen of them died. Small birds should not be so vulnerable; they can change direction quickly to avoid a collision. Large birds are much more at risk. Heavy and cumbersome flyers, they will crash into anything which appears suddenly in their flight path. It’s no surprise that Ireland’s largest bird, the mute swan, is the one most prone to collisions.

In 1983, I began a study of swans around Dublin. By 1994, 292 deaths had been recorded. The causes of death were apparent in 156 cases. Six birds had been shot, six had swallowed anglers’ lead weights and five had been savaged by dogs. Violent deaths can be ‘natural’: six swans died in fights with rivals. There were a few freak cases: one bird choked on a bread-crust, another died during surgery. However, the numbers dying from such causes were tiny compared to those from collisions.

Of 1,315 ringed swans, 14% were recorded in collisions but this was just the tip of an iceberg. Few such incidents ever come to light. Eleven birds had struck bridges and, in 10 cases, a building was the obstacle. Electricity cables presented the greatest hazard; these accounted for 84 accidents.

Ninety-five collision deaths were logged. Overall, at least one swan in three becomes a collision victim. Similar results were recorded in British studies.

Despite the high death rate, the mute swan population remains stable; enough cygnets fledge each year to compensate for the losses. Other large birds are not so lucky. Migrating storks are particularly vulnerable in Europe. So are bustards. The population of Ludwig’s bustard has declined rapidly due to collisions with power lines in Africa, so much so that there are fears for the species’ survival.

Collisions are a serious problem just about everywhere. So what can be done to reduce the carnage? Professor Graham Martin of the University of Birmingham has studied the bird collision problem in depth. His paper, Understanding Bird Collisions with Man-make Objects: a Sensory Ecology Approach, has just appeared in the ornithological journal Ibis. He talked about his findings last week on RTÉ’s Mooney Show.

Electrical cables are especially difficult for a wing guided by an eye to see. ‘Game guards’, in the form of cork tiles metal balls or ‘pigtails’, are sometimes placed on wires where collisions tend to occur. These should make the cable more visible to birds but nobody knows if they actually do.

Martin argues that, although something is visible to us, it is not necessarily so for birds. They look at the world differently. Their eyes and fields of vision are quite unlike ours. The same is true of the way they process visual information and assess risk. A bird flying over a wood, for example, does not expect to find a mast protruding from the trees or to encounter a cable when flying along a river. Birds have learned to rule out obstacles in such situations and so their attention when in flight tends to be elsewhere. No eye is all-seeing and fast moving creatures are prone to ‘motion smear’.

To deal with this problem, Martin argues, we must get inside the bird’s head and try to see things as it does. Obstacles, he suggests, might be painted in sharp contrasting colours, a suggestion which won’t please the architects of elegant suspension bridges. Game-guards and marking devices should not be static but moving; movement attracts attention. Decoys on the ground might lure flying birds into landing before they encounter a cable. Aural alerting systems could be effective in some situations.

The recent Kerry case, however, does not support his thesis. A three-year old eagle should have ‘known the ropes’. Yet it collided with the moving blade of a noisy windmill.